How Chloride-Rich Scrubber Service Changes Mist Eliminator Design

Mist eliminators in chloride-rich wet scrubbers operate in a difficult environment.

The separator must handle:

• corrosive liquid droplets;
• high humidity;
• dissolved salts;
• possible crystallization;
• suspended solids.

Examples may include scrubbers using:

• chloride-containing process liquid;
• saline water;
• seawater-based systems.

The challenge is not simply choosing a corrosion-resistant material.

Chloride-rich liquid can also affect:

• fouling;
• drainage;
• wash strategy;
• long-term mechanical reliability.

A separator that survives chemically but plugs rapidly is still an unsuccessful design.

Chloride Service Is More Than a Material Question

When chloride is mentioned, engineering discussions often immediately move to:

“SS304 or SS316L?”

That is only part of the problem.

The full separator duty should consider:

• chloride concentration;
• pH;
• temperature;
• oxygen content;
• wet-dry cycling.

These conditions affect corrosion risk.

But chloride-containing droplets can also leave salt deposits after evaporation.

The separator may therefore experience both:

• corrosion;
• crystallization.

Material and geometry need to be reviewed together.

Salt Concentration Can Increase Inside the Demister

The scrubber liquid may be below its salt saturation limit.

After droplets are captured, however, some water can evaporate from the thin liquid film.

Salt concentration increases locally.

Crystals may form on:

• wires;
• vane surfaces;
• support members.

This means a process that appears “fully liquid and no solids” can still create solid deposits inside the demister.

Fine mesh is particularly sensitive because small passages can become restricted rapidly.

Wet-Dry Cycling Can Accelerate Deposition

Some scrubbers operate continuously wet.

Others experience:

• startup;
• shutdown;
• intermittent washing.

During drying periods, captured saline liquid can leave crystalline deposits.

When the plant restarts, the deposits may partially dissolve and recrystallize.

Repeated cycles can create hard scale.

This is why the maintenance history matters.

A separator that operates acceptably during continuous service may foul more severely in a frequently cycled unit.

Stainless Steel Requires Careful Review

Chloride-containing environments can be aggressive toward stainless steel under some:

• temperature;
• concentration;
• crevice conditions.

The active mesh is not the only concern.

Crevice-like regions may exist around:

• clamps;
• frames;
• fasteners;
• support contacts.

A corrosion-resistant main mesh with unsuitable small components can still develop failure.

Exact material selection should therefore be based on the actual chloride environment rather than a generic “stainless steel is corrosion resistant” assumption.

Plastics Can Avoid Some Corrosion Problems

Materials such as:

• PP;
• PVDF

may be attractive in corrosive scrubber systems.

However, polymer selection introduces mechanical questions:

• operating temperature;
• stiffness;
• creep;
• support spacing.

The correct material must survive chemically and maintain separator geometry over time.

A chemically resistant separator that sags or deforms does not provide reliable performance.

Fine Wire Mesh Can Be Vulnerable to Salt Fouling

High-surface-area mesh provides strong droplet capture.

It also provides many sites for:

• evaporation;
• crystallization.

As salt accumulates:

• voidage decreases;
• pressure drop rises;
• drainage slows.

The separator may then flood at a lower gas load than when clean.

If salt deposition is expected, maximizing clean-condition collection efficiency may not be the best long-term design objective.

Open Vane Geometry Can Improve Maintainability

Vane separators generally provide larger flow passages.

This can improve:

• washability;
• salt-fouling tolerance;
• drainage.

They may be attractive where:

• droplets are sufficiently large;
• liquid loading is high;
• fouling risk dominates.

The tradeoff is that very fine droplets may require additional polishing.

A staged arrangement may therefore be useful in some chloride-rich services.

Wash Water Chemistry Matters

A demister wash system should not introduce more salts than it removes.

If the wash water itself contains:

• high chloride;
• hardness;
• suspended solids,

the cleaning system can contribute to deposition.

Fresh-water rinsing may sometimes be useful, depending on the process.

The wash strategy should consider both:

• deposit solubility;
• water quality.

Drainage Must Prevent Concentrated Salt Pockets

Poor drainage allows captured liquid to remain inside the separator.

Water evaporates.

Salt concentration rises.

Crystallization begins.

Therefore, support geometry and separator orientation become particularly important.

Avoid:

• low pockets;
• compressed mesh zones;
• blocked drainage channels.

A small drainage defect can become a major salt-deposition location.

Deposit Pattern Can Reveal the Mechanism

During shutdown, inspect where salts accumulate.

Heavy deposits near:

• vessel wall may indicate wall flow;
• support bars may indicate drainage obstruction;
• one side may indicate gas maldistribution.

Document the pattern before washing.

The salt layer provides useful evidence about vessel hydraulics.

Differential Pressure Provides an Early Warning

Salt fouling often develops progressively.

A clean pressure-drop baseline can help identify the onset.

If DP rises at the same gas load over time, available open area is probably decreasing.

Cleaning before severe blockage can be much easier than waiting for the pad to become fully packed with crystals.

Design for Cleaning From the Beginning

If salt fouling is expected, the separator should be designed around maintenance.

Consider:

• wash access;
• nozzle coverage;
• removable segmentation;
• drainage;
• inspection.

A separator that has slightly lower theoretical clean efficiency but can be maintained easily may provide much better long-term plant performance.

What Process Data Matters?

Useful information includes:

• chloride concentration;
• pH;
• temperature;
• gas flow;
• liquid loading;
• solids;
• expected evaporation;
• wash-water source;
• required outlet carryover.

Material selection should be confirmed from actual chemistry.

Final Engineering Perspective

Chloride-rich scrubber service combines corrosion and fouling risks.

The correct mist eliminator therefore cannot be selected from material compatibility alone.

The design must also consider salt concentration, evaporation, crystallization, drainage, washability, pressure-drop growth, and mechanical stability.

Long-term operating reliability is the real performance target.